The present invention relates to a hanging, rotating solar concentrating device wherein reflective sheets of the device are protectively furled. The present invention employs reflective sheets that are hung to form a catenary trough capable of concentrating light. The reflective sheet elements of the present device may be furled, to protect them from damage in wind, rain, or dust. The present device may concentrate light on a photovoltaic cell, thus generating electricity and heat at the photovoltaic cell. Embodiments of the present invention may include a novel means for removal of heat from the photovoltaic cell. The present device is balanced about its vertical axis of rotation, thus requiring minimum power to rotate. Some solar concentrating devices of the prior art will now be described and contrasted to the present invention.
In U.S. Application US 20100058703, Werner and Funai describe a reflective parabolic trough scheme that is commonly employed in the prior art, wherein a reflective trough element is parabolic, supported from underneath, and rotated about an axis that is coincident with the focal line of the trough, which is horizontal. Such a system requires a rigid, expensive reflective element and a strong, expensive structure to withstand wind, as well as floor area dedicated to the device. The present invention includes a reflective trough element that is catenary and is and rotated about a vertical axis.
In U.S. application Pat. No. 4,236,399, Williams and Skaggs present a method of forming a parabolic solar concentrating metal trough. Metal troughs are commonly used in the prior art, and are relatively heavy and expensive and require a heavy supporting structure. The present invention employs a solar concentrating trough that is made of less expensive and lighter materials than troughs typical of the devices described in U.S. Pat. No. 4,236,399. The present invention forms a solar concentrating trough in a simpler method than the method of U.S. Pat. No. 4,236,399 (i.e. —the present invention forms a solar concentrating trough by gravity).
In U.S. Application 20100206379, Littau, Maeda, and Cheung present an embodiment of a concentrating device that includes a parabolic reflector that is mounted on a rotating frame that may rotate about a vertical axis wherein the frame is supported from below (i.e. —the frame is supported from underneath). Such a device employs an expensive parabolic trough element. Such a device requires a strong, expensive structure to withstand wind, and floor area dedicated to the device. The surface upon which the frame is mounted must be level and/or prepared for the application. The present invention includes a catenary reflector that is mounted on a rotating frame that rotates about a vertical axis. Embodiments of the present invention may include a rotating frame that is hung from above.
In PCT Application WO2012042407, Adigiouzel and Kourtis present an embodiment of a concentrating device that includes a catenary reflector that is mounted on a rotating frame that may rotate about a vertical axis that is supported by wires, wherein the reflective surfaces of the device are comprised of strips that are interleaved in order to minimize wind load. Although an interleaved surface encounters a lower wind load than a non-interleaved surface, interleaving does not lessen wind load sufficiently to prevent damage to reflective surfaces by wind, nor does it protect reflective surfaces from damage by moisture and dust; thus the device of WO2012042407 cannot be practically employed. The present invention includes a catenary reflector that is protectively furled. During furling, reflective surfaces that are lightweight and inexpensive may be fully protected from wind, moisture, and dust.
In U.S. Pat. No. 6,237,241, Aaron and Nock present various concentrators that are hung from wires. The concentrators presented in U.S. Pat. No. 6,237,241 do not include catenary reflectors. The concentrators presented in U.S. Pat. No. 6,237,241 are subject to wind damage and transfer of wind loads. The present invention includes a catenary reflector that is protectively furled, that is not susceptible to wind damage, and transfers minimal wind load to the supporting structure when furled.
In U.S. Pat. No. 5,851,309, Kousa presents a catenary concentrator that does not rotate. Light is reflected by vertical “directing” reflectors to the stationary catenary reflector. Such a system requires expensive and numerous “directing” reflectors and causes the catenary reflector to be inefficient due to shading and cosine losses. In U.S. Pat. No. 5,851,309, reflective surfaces of the device are protected in two ways. One method of protection involves housing the reflective surface inside a transparent structure. The other method of protection involves building the device from strong materials. Both protection methods presented in U.S. Pat. No. 5,851,309 are expensive. The present invention uses an inexpensive method (i.e. —furling) to protect reflective surfaces. In U.S. Pat. No. 5,851,309, a catenary reflective surface is partially spooled and unspooled from a roller to achieve an adjustment of focal length. In the present invention, a catenary reflective surface is fully spooled and unspooled from a spool to achieve protection of reflective surfaces and to effect minimization of wind load transfer to the supporting structure.
In U.S. Application Pat. No. 5,885,367, Brown and Whalen present a device including reflector panels that are wrapped around booms. The device of U.S. Pat. No. 5,885,367 includes planar reflective elements that are wrapped to conserve space during transport in spacecraft. The present invention includes catenary reflective elements that are protectively wrapped and intended for terrestrial applications. The wrapped reflective surfaces of the device of U.S. Pat. No. 5,885,367 are unwrapped only once during operation (i.e.—after launch). The wrapped reflective surfaces of the present invention are wrapped, unwrapped, rewrapped, etc. many times over the course of use. The wrapped reflective surfaces of the device of U.S. Pat. No. 5,885,367 are unwrapped by manual actuation. In some embodiments of the present invention, reflective surfaces may automatically wrap in response to damaging environmental factors, and un-wrap in response to favourable environmental factors.
In NASA document NASA-CR-192080, Huff, Remington, and Tang present a reflector intended for lunar applications that includes a catenary reflective surface that is partially spooled and unspooled from a roller to achieve an of adjustment of focal length, wherein the reflector assembly is supported from underneath. In the present invention, a catenary reflective surface is fully spooled and unspooled from a spool to achieve protection of reflective surfaces and minimization of wind load transfer to associated structures. In some embodiments of the present invention, rotating parts may be supported from above.
In European application EP 2111520, Diemunsch presents a device for removal of heat from a photovoltaic cell wherein the photovoltaic cell is mounted on a water cooled block. Such a heat removal method requires an auxiliary fluid delivery system. Such a device is difficult to incorporate into a rotating receiver/concentrator. Diemunsch also refers to the inefficient prior art method commonly used to remove heat from photovoltaic cells, wherein the photovoltaic cell includes an aluminum heat sink heat exchanger surface on the back of the photovoltaic cell. In the present invention the photovoltaic cell is immersed directly in a boiling cooling medium thus allowing efficient transfer and obviating an external circulation system.
In PCT application WO2004042828, Osipov, G. Rubin, and L. Rubin present a device that includes a photovoltaic cell that is cooled by a heat pipe. The heat pipe is attached to “a heat transfer surface” of the photovoltaic (i.e.—the heat pipe is external to the photovoltaic cell). The heat transfer rate of such a system is limited by conductivity at the “heat transfer surface”. The heat transfer rate of such a system is limited by the available “heat transfer surface” area (i.e.—the “back” of the photovoltaic cell). The photovoltaic cooling method of the present invention differs from PCT application WO2004042828 in that the photovoltaic cell that is immersed in a heat pipe. All surfaces of the photovoltaic cell of the present invention are in contact with the cooling medium.
In PCT application 2011012917, F. Flechsig, Voegeli, and T. Flechsig, present a device that includes a photovoltaic that is cooled by a vapourizing fluid wherein photovoltaic wafers are glued to a heat exchanger carrying the vapouizing fluid. The present invention differs from PCT application 2011012917 in that it includes a photovoltaic cell that is immersed in a heat pipe.
In PCT application WO2011134759, Capan discloses a solar trough system that rotates about its focus and includes counterweights to the reflective trough and related parts, so as to minimize the energy required to rotate reflective parts. The present invention includes parts that are either balanced about the axis of rotation, or counter-weighted by congruent parts. The device of WO2011134759 rotates about a horizontal axis. The present invention rotates about an axis of rotation is about a vertical. The counterweights of WO2011134759 provide one function only (i.e.—to provide counter-weight). Such a system includes expensive counterweights that serve no function other than balancing useful parts. “Congruent part” counterweights of the present invention provide two functions; to provide counter-weight as well as to provide a function as component of either the solar concentration means, the furling means, the furling mechanism, the balancing of parts about the central vertical axis, the immersed photovoltaic heat pipe receiver design, the supporting means, the positioning means, or the ballast of the device.